Composite aluminum alloy



United States Patent 3,312,536 COMPOSITE ALUMINUM ALLOY Irwin Broverman,Grange, C0nn., assignor to Olin Mathieson Chemical Corporation, acorporation of Virginia No Drawing. Original application June 19, 1963,Ser.

No. 288,870. Divided and this application May 26,

1964, Ser. No. 377,161

4 Claims. (Cl. 29-1835) This application is a division of co-pendingapplication Ser. No. 288,870 filed June 19, 1963.

The present invention relates to a new and improved process for forminga composite aluminum alloy and to the resultant composite. Moreparticularly, the present invention resides in a novel, convenient andexpedient process for forming a composite aluminum alloy which combineshigh strength with good bright anodizing characteristics.

It is highly desirable to provide aluminum alloys which combine goodbright anodizing characteristics and high strength. The term brightanodizing is used herein in the conventional sense, that is, a finishingprocess consisting of, for example, optional bufling and polishing ofthe work piece, chemical brightening by, for example, a nitric acid typesolution, anodizing in an electrolyte, such as sulfuric acid and'sealingin hot water containing the conventional additives, if desired.

The commercially available aluminum alloys thatare capable of providinghigh quality, high specular finish upon bright anodizing are generallyrelatively low strength alloys. The base-purity of such alloys isrelatively high and the total alloying content relatively small. Thefollowing table shows typical commercial alloys amenable to brightanodizing. In the following table, and throughout the presentspecification, the alloy designations are those assigned by the AluminumAssociation.

Typical yield strength for the foregoing group of alloys in the fullyannealed condition ranges from about 5000 p.s.i. for alloy 5257, theleast alloyed material, to about 7000 p.s.i. for alloy 5357, thestrongest of the group. At the present time, the bright anodized finishobtainable with alloy 5457 is a standard generally accepted by thealuminum finishing industry.

Heretofore, it has been found possible to increase the magnesium contentof the aluminum base alloy to about 2.5 percent, thereby effectivelyincreasing the strength and yet maintaining bright anodizingcharacteristics comparable with those of alloy 5457. A yield strength ofabout 12,000 p.s.i. in the fully annealed condition is obtained in suchan alloy. However, when the magnesium content is increased beyond 2.5percent in order to further strengthen the material, it is found thatthe brightness, clarity and specularity of the bright anodizing finishare depreciated significantly, unless the impurity content issignificantly lowered.

In order to overcome these limitations and, in fact, optimally toachieve even higher strength properties, it has been suggested to clad ahigh strength core material with a good bright anodizing coatingmaterial; however, when a high strength aluminum basealloy containingfrom 2 to percent magnesium is heated, there is formed on the 3,312,536Patented Apr. 4, 1967 surface a harmful layer of surface oxide that isenriched in magnesium oxide. This layer makes the forge welding of thecladding layer to the core or backing extremely difficult or erratic.One method which has been suggested to overcome this difficulty is toinclude varying amounts of an additional alloying ingredient, such asberyllium in an amount up to about 0.5 percent, in the core material.While this effectively overcomes the difliculty, it is subject to thedisadvantages of requiring additional and often undesirable alloyingingredients.

Other methods for overcoming these limitations include (1) the use of acontrolled atmosphere for heating of the cladding and core materialsprior to the forge welding operation, and also (2) compounds, such assodium fluoborate may be added to the furnace atmosphere to reduce theoxide formation. These methods are expensive and may require specialequipment.

Accordingly, it is an object of the present invention to provide a noveland convenient process for achieving a composite aluminum alloycombining high strength with good bright anodizing characteristics.

It is a further object of the present invention to provide a process asaforesaid for cladding a high strength aluminum alloy core material witha good bright anodizing aluminum coating.

It is a still further object of the present invention to provide aprocess as aforesaid which is simple, convenient and readily amenable tocommercial practices.

It is an additional object of the present invention to provide a processas 'aforesaid which enables the formation of new and improved highstrength. good bright anodizing aluminum alloy composites without thenecessity of utilizing undesirable or expensive or inconvenient alloyingmaterials.

Further objects and advantages of the present invention will appearhereinafter.

In accordance with the present invention it has now been found that theforegoing objects and advantages can be readily and convenientlyaccomplished and there is obtained a novel clad product, i.e., acomposite alloy, and a method for cladding a core material. Thecomposite alloy comprises an aluminum base alloy containing from 2 to 10percent magnesium with a coating consisting essentially of aluminum, andthe methodcomprises forming an assembly by superimposing said coating onsaid core, venting the air at the interface and integrating said coreand said coating.

The process of the present invention results in a high strength, goodbright anodizing aluminum composite which achieves numerous heretoforeunobtainable and often surprising advantages. These advantages will bediscussed and elaborated upon throughout the present specification andexamples. Surprisingly, the characteristics of the composite in thefully annealed condition are: a minimum yield strength of 14,000 p.s.i.,a minimum tensile strength of 35,000 p.s.i., and a minimum elongation of15 percent in two inches. In addition, surprisingly, the brightanodizing characteristics of the resultant composite are at least asgood as, and generally superior to, those of the cladding alloy insingle form.

The alloy obtained in accordance with the process of the presentinvention is especially useful in the preparation of formed articlessince it has the characteristics necessary for use therein, such as goodformability and fine grain size control.

-It has been further found, surprisingly and unexpectedly, that thepresent invention renders it readily possible to produce sound, highstrength bonds by hot rolling a high strength aluminum-magnesium coreand good bright anodizing aluminum-magnesium surface cladding. This isquite surprising in view of the simple process employed a) in thepresent invention and in view of the common belief heretofore that themagnesium oxide formed during the heating of the two aluminum-magnesiumalloy components render it extremely difficult, if not impossible, toobtain a high strength pressure weld by hot rolling methods.

In accordance with the present invention, the core material comprises ahigh strength aluminum base alloy containing from 2 to 10 percentmagnesium. Typical of such alloys are the following:

7 aluminum content is preferably at least 95 percent.

material for the hot rolling operation.

TABLE 2 Content, Percent Alloy Mg Mn Cr 5086 4. O. 45 0.15 5083" 4. 0.65 0.15 5456 5.1 0.75 0. Undesignated 7. 0

The typical yield strength in the fully annealed condition of the abovealloys ranges from 17,000 p.s.i. for alloy 5086 to 21,000 p.s.i. foralloy 5083 and to 23,000 p.s.i. for alloy 5456. The correspondingtensile strengths of these alloys are typically 38,000 p.s.i. for alloy5086, 42,000 p.s.i. for alloy 5083 and 45,000 p.s.i. for alloy 5456.

The core material may, of course, be any conventional high strengthaluminum base alloy containing from 2 to 10 percent magnesium andpreferably at least 85 percent aluminum. Additional alloying ingredientsmay, of course, be added to the core material if desired in order toobtain particular characteristics, 'as, for example, manganese, andchromium may be added to obtain additional strength and provide bettergrain size control. The use of undesirable alloying ingredients is notnecessary in accordance with the present invention in order to obtain agood bond between the core material and the coating material. Typicaland conventional alloying elements often used and compatible inaccordance with the present invention include the following withrepresentative ranges thereof: manganese, from 0.15 to 1.0 percent, andchromium from .05 to .30 percent.

The cladding material which may be employed consists essentially ofaluminum, i.e., a good bright anodizing material, such as an aluminumalloy containing up to 2.5 percent magnesium, and preferably from 0.01to 2.5 percent, or alternatively, high purity or super purity aluminum.Where 'an aluminum base alloy is employed the Conventional additives orother alloying materials may, of course, be included in the claddingmaterial, provided that the good bright anodizing characteristics arenot impaired, for example, any of the following or mixtures thereof:copper, up to 0.3 percent; manganese, up to 0.45 percent; iron, up to0.17 percent; silicon, up to 0.12 percent; i.e., from about 0.001 up tothe upper figure given. Typical coating alloys are those listed in Table1 above.

The optimum cladding thickness is dependent upon the final buffingrequirements. Generally speaking, it is not desirable to employ coatingsabove percent since the thicker the coating the less the effect of thehigh strength core material is felt, and preferably from 5 to 20percent.

In the i preferred operation, the mating surfaces are cleaned in theconventional manner, such as chemical cleaning and wire brushing. Thecore material does not need to be hot worked prior to assembly with thecladding The cladding is superimposed on the core to form an assembly,and the assembly is peripherally integrated leaving an unintegratedperipheral portion in the posterior section of said assembly, e.g.,- thecore material is fusion Welded to the coating material around its entireperiphery leaving an unwelded area in one portion thereof. This unweldedarea or exit vent serves to permit the escape of entrapped air ormagnesium oxide. Once this is done the composite or assembly may be hotrolled by commercial rolling equipment with entrapped air escapingthrough the exit vent. The cladding material is generally hot rolled tothe required gauge that will give the necessary percentage of thethickness of the final composite. Heating of the assembly for rollingmay be done in a natural air atmosphere.

Alternatively, but less desirable, the initial fusion Welding may beomitted and the core and coating material superimposed to form acomposite, followed by an ironing pass at slow speed, i.e., less thanabout 10 feet per minute in the absence of rolling lubricant and with areduction on the order of about less than 10 percent. This ironing passserves to exhaust entrapped air by pressure, brings the cladding andcore materials into intimate contact, i.e., a partial mechanical bond,and effectively precludes the contamination of the interface by rollinglubricant during the subsequent reduction to achieve a sound pressureweld. Subsequent passes may then fully weld the components.

In the preferred operation a minimum hot rolling reduction of about 30percent is preferred prior to further hot rolling to final gauge.

In accordance with the present invention good bonds were obtained at hotrolling temperatures ranging from 450 to 950 F.

The resultant pressure welded interface of the composite alloy ischaracterized by no bond blistering developing during the thermaltreatments of the composite alloy including high temperature annealingand no separation at the interface during extreme bending or drawing andcupping tests in which the pressure weld was held. In addition, thetensile properties of the composite alloy at 0.040 to 0.050 inch gaugewere virtually equal to those of the core alloys in single alloy formdespite a surface cladding of 8.5 percent of the much softer brightanodizing alloy. This characteristic is quite surprising and unexpectedand means, in effect, for all practical purposes, the mechanicalproperties of the core alloys may be used to approximate the strengthand formability. This is a particular and useful advantage of thepresent invention. Therefore, the composite alloy is characterized bythe apparent strength of the core material and the bright anodizingcharacteristics of the cladding material.

Still further, the bright anodizing characteristic-s of the claddingalloy, including brightness, clarity, specularity and freedom fromtextural and structural streaking were noticeably improved as comparedwith the same alloy in single form produced by normal productionmethods. This improvement prevailed throughout the entire temperaturerange of hot rolling.

Other and significant advantages of the present invention include theattainment of good brig-ht anodizing characteristics in the conventionalbright anodizing alloy with a wide latitude of control in thefabricating operations. These cladding alloys were not as sensitive tothe effects of thermal treatment as they normally are in the singleform. In addition, fine grain size control was readily achieved in thecomposite.

The present invention and improvements resulting therefrom-will be morereadily apparent from a consideration of the following illustrativeexamples.

Example 1.-C0re alloy 5086, cladding alloy 5457 The above core andcladding alloys were used in samples 9 inches long, 6 inches wide and1.125 inches thick for alloy 50% and 0.125 inch thick for alloy 5457.The mating surfaces of the alloys were cleaned and were brushed. Thecladding alloy was superimposed on the core alloy to form an assemblyand then sandwich welded along the entire lead end, sides and tail,except for a small vent in the tail end. The composite was then hotrolled by a light pass at 30 feet per minute followed by heavy passes atfeet per minute. The temperatures ranged from 850 F. to 500 F The finalgauge of half of the samples was 0.250 inch, and half 0.150 inch. Thesamples were then cold rolled and annealed. The bright anodizingcharacteristics of the resultant composite were visually observed to besuperior to those of the cladding alloy in single form in respect tospecularity, clarity and uniformity.

The resultant composites had the following characteristics:

Yield strength, p.s.i 17,00020,0= Tensile strength, p.s.i 36,0003'S,000Elongation in two inches, percent 21-27 Additional characteristics ofthe composite were: the high ductility of the composite, as evidenced bythe large value of elongation in the tensile test, in combination withthe high strength levels imparted by the core material, enabled severeforming operations to be accommodated; the grain size of the cladding inthe composite was observed to be generally finer than the same materialin single a'lloy form; the integrity and soundness of the bondingbetween the core alloy and the cladding was proved by the fact that noseparation occurred during severe forming, such as by Erichson bulgetesting, by cupping, by pulling in tension to rupture, and by bendingwith the cladding either in tension or compression; and no bondblistering during thermal treatments of the composite, as, for example,high temperature annealing subsequent to cold rolling.

Further, the cladding and core materials were found to be compatiblegalvanically. The cladding provided cathodic protection for the corematerial.

Example 2.-C0re alloy 5086, cladding alloy 5557 Ina manner after Example1 a composite was prepared from the above core and cladding alloys. Theresultant composite had characteristics similar to that of Example 1,with the following specific values found:

Yield strength, p.s.i 17,000-20000 Tensile strength, p.s.i36,0003-8,0-0=0 Elongation in two inches, percent 21-27 Example 3.-C0realloy 5083, cladding alloy 5457 In a manner after Example 1 a compositewas prepared from the above core and cladding alloys. The resultantcomposite had characteristics similar to that of Example 1, with thefollowing specific values found:

Yield strength, p.s.i 21,000 Tensile strength, p.s.i. 4 2,000 Elongationin two inches, percent 22 6 Example 4.C0re alloy 5083, cladding alloy5557 In a manner after Example 1 a composite was prepared from the abovecore and cladding alloys. The resultant composite had characteristicssimilar to that of Example 1, with the following specific values found:

Yield strength, p.s.i 21,000

Tensile strength, p.s.i 42,000

Elongation in two inches, percent 22 Example .C0m-parative Example 1 wasrepeated, with the exception that prior to hot rolling the composite waswelded along the entire lead end, sides and tail, with no vent beingprovided in the tail end. Separation of the cladding and core materialsoccurred upon the materials exiting from the rolls.

This invention may be embodied in other forms or carried out in otherways without departing from the spirit or essential characteristicsthereof. The present embodiment is therefore to be considered as in allrespects illustrative and not restrictive, the scope of theinventionbeing indicated by the appended claims, and all changes which comewithin the meaning and range of equivalency are intended to be embracedtherein.

What is claimed is:

1. A composite aluminum alloy having a metallurgically integrateddissimilar core and cladding, said core consisting essentially of from 2to 10% magnesium,balance essentially aluminum, said cladding consistingessentially of from 0.01 to 2.5% magnesium, balance essentiallyaluminum, said composite having, in the fully annealed condition, aminimum yield strength of 14,000 p.s.i., a minimum tensile strength of35,000 p.s.i. and a minimum elongation of in two inches wherein saidcladding has a thickness less than of the thickness of the composite 2.A composite alloy according to claim 1 wherein said cladding has athickness from 5 to 20% of the thickness of the composite.

3. A composite alloy according to claim 1 wherein said core materialcontains from 0.15 to 1.0% manganese and from 0.05 to 0.30% chromium.

4. A composite alloy according to claim 3 wherein said cladding containsup to 0.3% copper, up to 0.45% manganese, up to 0.17% iron and up to0.12% silicon.

References Cited by the Examiner UNITED STATES PATENTS 2,354,006 7/1944Gauthier 29197.5 2,3 83,511 8/ 1945 Reynolds 29-197.5 3,093,459 6/1963Siebel 29-l97.5

HYLAND BIZOT, Primary Examiner.

1. A COMPOSITE ALUMINUM ALLOY HAVING A METALLURGICALLY INTEGRATEDDISSIMILAR CORE AND CLADDING, SAID CORE CONSISTING ESSENTIALLY OF FROM 2TO 10% MAGNESIUM, BALANCE ESSENTIALLY ALUMINUM, SAID CLADDING CONSISTINGESSENTIALLY OF FROM 0.01 TO 2.5% MAGNESIUM, BALANCE ESSENTIALLYALUMINUM, SAID COMPOSITE HAVING, IN THE FULLY ANNEALED CONDITION, AMINIMUM YIELD STRENGTH OF 14,000 P.S.I., TO A MINUMUM TENSILE STRENGTHOF 35,000 P.S.I. AND A MINIMUM ELONGATION OF 15% IN TWO INCHES WHEREINSAID CLADDING HAS A THICKNESS LESS THAN 20% OF THE THICKESS OF THECOMPOSITE.